The phone is equipped to use multiple LTE spectrum bands, though U.S. carriers don't offer foreign LTE roaming yet

U.S. buyers of the iPhone 5 won't have international LTE roaming when the highly anticipated device hits the street on Friday, but information from Apple, the FCC and carriers offers glimmers of hope that foreign LTE networks will be in reach eventually.

The new iPhone, which is set to ship on Friday, comes in at least two different versions, each of which is equipped to use a long list of cellular frequencies. To sell the iPhone 5 in its home country, Apple got many certifications for various types of radios from the U.S. Federal Communications Commission.

One thing missing from those approvals is LTE Band 3, a set of frequencies around 1800MHz that is expected to be used by carriers in many countries, especially in Europe. That band could be critical for LTE use outside the U.S., because two other LTE bands popular in Europe -- at 800MHz and 2.6GHz -- aren't built into the iPhone 5 at all. Yet it turns out that Band 3 may be there anyway.

LTE promises to bring much higher data speeds to mobile users around the world over the next few years. There are 299 carriers either operating, building or planning LTE networks today with the most popular form of the technology, called frequency-division duplex, according to Ovum analyst Daryl Schoolar. But in the near future, few if any users will be able to enjoy LTE speeds outside their home countries, partly as a result of so many different spectrum bands being used. At least 10 different LTE bands are defined worldwide.

In keeping with Apple's practice of paring down its models, the iPhone 5 is on the leading edge of multiple frequency support. At least one of its models includes hardware for five LTE bands plus 11 2G and 3G bands. That may pay off eventually for foreign LTE roaming.

The technical specs on Apple's site for the CDMA version of Model A1429 -- intended for Sprint Nextel and Verizon Wireless, plus KDDI in Japan -- list support for LTE Bands 1, 3, 5, 13 and 25, plus several sets of frequencies for older GSM, UMTS and CDMA networks. But the only LTE bands that the FCC has certified for the product are the last three: Bands 5 and 25, which will be used for LTE on Sprint's network, and Band 13, where Verizon operates the technology.

Apple's failure to support LTE Band 3 on its first LTE tablet, the iPad 3, helped to cause hand-wringing over the long-term prospects for LTE roaming. In Australia, where Telstra uses Band 3, Apple even got into legal hot water over advertising the iPad as a 4G device.

The new iPhone includes Band 3 in both the CDMA and GSM versions of Model A1429. The GSM version is intended for use on Telstra as well as on LTE networks in Germany, the U.K., South Korea, Japan, Singapore and Hong Kong. Both versions also include Band 1, which is used by some Asian carriers. In fact, because the FCC's documentation only uses the designation A1429, those two versions may be identical in hardware terms, with different radios activated. Apple did not respond to questions about the model names.

Apple doesn't need FCC approval to build in radios for bands that aren't used in the U.S., according to people familiar with its regulations. That's because cellphones don't "talk" unless a network talks to them first. Placed in any environment, a phone will passively listen for signals from any nearby network it can pick up, and respond if it can, said analyst Tim Farrar of TMF Associates. By itself, the phone won't pose a threat of interference. So Apple may be selling U.S. consumers an iPhone 5 with activated, fully capable LTE Band 1 and Band 3 radios. The FCC did not respond to a request for comment.

The bad news is that none of the U.S. iPhone 5 carriers offers international roaming on LTE, at least for now. At launch, iPhone 5 travelers will be limited to using older GSM, HSPA or CDMA networks. One of the carriers, Verizon, did say it plans to add global LTE roaming in the future.

"As there are many LTE frequencies currently being deployed around the world, Verizon will be surveying which markets line up best with the frequencies available in our version of the iPhone 5," spokeswoman Brenda Raney said, via email.

Replacing the phone's SIM card with one from the foreign service provider may not be much of an alternative. Verizon allows any customer in good standing for at least 60 days to unlock their phone and swap in another SIM. However, Sprint said its subscribers could not use another carrier's SIM, and AT&T has another set of restrictions on unlocking. AT&T subscribers have to wait out their two-year contracts, upgrade to a new phone, or pay an early termination fee before the carrier will unlock a phone. There is no unlocked iPhone 5 for sale yet. Apple's use of a new, smaller "nano-SIM" card may also complicate this type of roaming solution.

However, it's likely that wherever they can, carriers ultimately will include LTE data service in their roaming deals, Schoolar said. International data roaming plans typically are denominated in bits.

"There doesn't really seem to be much concern on the part of the operator on how you suck up that amount of data," Schoolar said. "You can suck it up slow with EDGE or fast with LTE."

Meanwhile, the FCC documentation for the new iPhone also revealed what may be hints about future LTE rollouts within the U.S. Apple lists Model A1428 with LTE bands 4 and 17, which corresponds to the spectrum being used by its designated carriers, AT&T and three Canadian carriers. But at the FCC, that model also got certifications for LTE Bands 2 and 5. Band 2 is around 1.9GHz and Band 5 around 850MHz. It's likely that Apple included radios for those bands so AT&T can later convert spectrum it holds in those frequencies to LTE, analysts said.